From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 4BD966B004D for ; Wed, 24 Jun 2009 19:10:51 -0400 (EDT) Date: Wed, 24 Jun 2009 16:10:28 -0700 From: Andrew Morton Subject: Re: [RFC] Reduce the resource counter lock overhead Message-Id: <20090624161028.b165a61a.akpm@linux-foundation.org> In-Reply-To: <20090624170516.GT8642@balbir.in.ibm.com> References: <20090624170516.GT8642@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: kamezawa.hiroyu@jp.fujitsu.com, nishimura@mxp.nes.nec.co.jp, menage@google.com, xemul@openvz.org, linux-mm@kvack.org, lizf@cn.fujitsu.com List-ID: On Wed, 24 Jun 2009 22:35:16 +0530 Balbir Singh wrote: > Hi, All, > > I've been experimenting with reduction of resource counter locking > overhead. My benchmarks show a marginal improvement, /proc/lock_stat > however shows that the lock contention time and held time reduce > by quite an amount after this patch. That looks sane. > ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > class name con-bounces contentions > waittime-min waittime-max waittime-total acq-bounces > acquisitions holdtime-min holdtime-max holdtime-total > ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- > > &counter->lock: 1534627 1575341 > 0.57 18.39 675713.23 43330446 138524248 > 0.43 148.13 54133607.05 > -------------- > &counter->lock 809559 > [] res_counter_charge+0x3f/0xed > &counter->lock 765782 > [] res_counter_uncharge+0x2c/0x6d > -------------- > &counter->lock 653284 > [] res_counter_uncharge+0x2c/0x6d > &counter->lock 922057 > [] res_counter_charge+0x3f/0xed Please turn off the wordwrapping before sending the signed-off version. > static inline bool res_counter_check_under_limit(struct res_counter *cnt) > { > bool ret; > - unsigned long flags; > + unsigned long flags, seq; > > - spin_lock_irqsave(&cnt->lock, flags); > - ret = res_counter_limit_check_locked(cnt); > - spin_unlock_irqrestore(&cnt->lock, flags); > + do { > + seq = read_seqbegin_irqsave(&cnt->lock, flags); > + ret = res_counter_limit_check_locked(cnt); > + } while (read_seqretry_irqrestore(&cnt->lock, seq, flags)); > return ret; > } This change makes the inlining of these functions even more inappropriate than it already was. This function should be static in memcontrol.c anyway? Which function is calling mem_cgroup_check_under_limit() so much? __mem_cgroup_try_charge()? If so, I'm a bit surprised because inefficiencies of this nature in page reclaim rarely are demonstrable - reclaim just doesn't get called much. Perhaps this is a sign that reclaim is scanning the same pages over and over again and is being inefficient at a higher level? Do we really need to call mem_cgroup_hierarchical_reclaim() as frequently as we apparently are doing? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org